Since nanosized semiconductor particles each have a particle diameter in the order of nanometers, it is known that a quantum size effect to increase band gap energy and so forth is produced, resulting in optical properties, exhibiting a light absorption property and light emission property, for example. Not only active studies of nanosized semiconductor particles have recently been made, but also studies of nanosized semiconductor particles such as CdSe/ZnS type nanosized semiconductor particles, Si/SiO2 system nanosized semiconductor particles and the like have been in progress for various uses such as displays or LED.
On the one hand, as a means to label a biosubstance, studied has been a method with a biosubstance labeling agent in which a molecular label substance was bonded to a marker substance. However, the marker substance used in the above-described method, such as organic fluorescence dyes, exhibited disadvantages of large degradation and short life during exposure to UV light, and resulted also in low emission efficiency and insufficient sensitivity.
Accordingly, attention has recently been focused on a method with nanosized semiconductor particles used as the above-described marker substance. For instance, studied has been a biosubstance labeling agent, in which a polymer containing a polar functional group is physically and/or chemically attached onto the surface of nanosized semiconductor particles (refer to Patent Document 1, for example).
On the other hand, also studied has been a biosubstance labeling agent in which an organic molecule is bonded to the surface of Si/SiO2 system nanosized semiconductor particles (refer to Patent Document 2, for example).
However, there appeared a problem against a biosubstance labeling agent employing these conventional nanosized semiconductor particles.
For example, nanosized semiconductor particles disclosed actually in Patent Document 1 with respect to the effect are (CdSe/ZnS system) nanosized semiconductor particles, but when they are used as a biosubstance labeling agent, those used as the biosubstance labeling agent have produced a problem since reduced environmental load together with minimized bio toxicity associated with a material used for the nanosized semiconductor particle, specifically CdSe, has been pointed out, though the particle surface is covered with organic molecules.
In the case of Si/SiO2 system nanosized semiconductor particles disclosed in Patent Document 2, the core is made of Si, but Si tends to be oxidized, depending on the environment despite the fact that a core made of Si is covered by a shell made of SiO2 (reaction between Si and oxygen in an aqueous dispersion) since nanosized semiconductor particles are commonly utilized in the presence of oxygen, whereby there is still room for improvement.
Patent Document 1: Japanese Patent O.P.I. Publication No. 2003-329686.
Patent Document 2: Japanese Patent O.P.I. Publication No. 2005-172429.